Printed Circuit Board or Card Comprising a Heating Wire

ABSTRACT

The invention relates to a printed circuit board or card comprising an electric circuit. In order to improve printed circuit boards of this type, the invention calls for at least one electrically conductive heating wire that can be connected to a voltage source to be provided on or in the printed circuit board or card.

STATE OF THE ART

The invention relates to a printed circuit board or card comprising an electric circuit according to the generic term of claim 1.

When such printed circuit boards are arranged in electric devices which are located outdoors, they are often exposed to severe temperature changes. This can lead to the formation of condensation water and therefore to short circuits within the electric circuit. Furthermore, the printed circuit board can expand in various ways according to the fluctuating temperatures, which can give rise to short circuits or contact separations in the electric circuit.

The object of the invention under consideration is therefore to further develop a printed circuit board or card of the type mentioned at the beginning that largely avoids the disadvantages described above.

According to the invention, this object is solved by means of the characterising features of claim 1.

ADVANTAGES OF THE INVENTION

The invention is based on the idea that at least one electrically conductive heating wire that can be connected to a voltage source is arranged on or in the printed circuit board or card. In this way, the card or printed circuit board can be constantly kept at a defined temperature by heating. The level of this temperature is coordinated to the particular case, and should not interfere with the function of the electric circuit and particularly that of its electric and electronic components. As a result of the heating, formation of condensation water and strongly changing thermal expansion of the printed circuit board or card are largely avoided, so that the circuit's susceptibility to faults is advantageously reduced.

Advantageous further developments and improvements of the invention specified in claim 1 are possible by means of the measures given in the dependent claims.

Particularly preferably, the heating wire is attached to the printed circuit board or card by means of wire-printing. While strip conductors on cards or printed circuit boards are normally manufactured by means of an etching process, i.e., the areas between desired strip conductors are etched away from copper film that has been applied to a support board, in the case of wire-printed circuit boards or cards, conductors made of an electrically conductive material are laid between connection points of the card arranged on the card and, for example, moulded into a block of an insulating compound together with the card in a sandwich structure. A method for producing such a wire-printed printed circuit board or card is known, for example, from DE 196 18 917 C1.

A particularly uniform temperature distribution results if the heating wire essentially extends across the entire surface of the printed circuit board or card in a meandering way.

Particularly preferably, the heating wire is formed by a resistance wire and connects connection points that are arranged on the printed circuit board or card and that are for the voltage source to one another.

DRAWING

In the following, an embodiment of the invention is depicted in the drawing and explained in more detail in the subsequent description. Shown in the drawing are:

FIG. 1 a perspective view of a printed circuit board, on which an electrically conductive heating wire is applied according to a first manufacturing step;

FIG. 2 a perspective view of the printed circuit board of FIG. 1 with the electrically conductive heating wire, on to which a covering insulation layer is applied according to a further manufacturing step;

FIG. 3 a perspective view of the printed circuit board of FIG. 1 in the completed state.

DESCRIPTION OF THE EXAMPLE EMBODIMENT

The electrically insulating printed circuit board indicated as a whole as 1 in FIG. 1 is preferably an etched printed circuit board, i.e., located on its surface are flat strip conductors made of copper, preferably developed by means of etching, which form an electric circuit but which are not shown for the sake of clarity.

According to a first manufacturing step, shown schematically in FIG. 1, an electrically conductive conductor, for example, in the form of a heating resistance wire 2, is applied to the printed circuit board 1 by means of wire-printing. The application of a conductor on to a printed circuit board 1 by means of wire-printing is known, for example, from DE 196 18 917 C1. In the case at hand, therefore, a combination of etched strip conductors with a heating resistance wire 2 is realised on the printed circuit board 1.

This wire can be a wire with an electrically insulating layer or one without an electrically insulating layer. An electrically insulated wire is particularly suitable for laying the heating wire in a meandering manner if the heating wire and the strip conductors are arranged on the same side of the printed circuit board. In this way, the manufacture can be simplified and unwanted electrical contact between the heating wire and the strip conductor can be avoided. Preferably, the wire is not insulated if the wire and strip conductors are arranged on different sides of the printed circuit board. If the strip conductors and heating wire are arranged on the same side of the printed circuit board, a non-electrically insulated heating wire can nevertheless be used if it is possible to ensure a distance between the strip conductor and the heating wire. The heating wire should preferably be kept at a distance from the strip conductor perpendicular to the two-dimensional extension of the printed circuit board. The distance here should naturally be selected in such a way that the total thickness of the completed printed circuit board does not become too large, but still just large enough that sufficient electrical insulation is insured. In the preferred embodiment, the strip conductor and the heating wire cross over each other in a top view of the printed circuit board or are arranged at a distance from each other, one on top of the other, perpendicularly to the two-dimensional extension of the printed circuit board.

In a further manufacturing step shown in FIG. 2, the ends of the heating resistance wire 2 are connected to, for example, two connection points 4 arranged on a side surface of the printed circuit board 1, preferably by means of welding, by means of which it is possible to create a connection to an external voltage source. The voltage source can, however, also be arranged directly on the printed circuit board 1, e.g., in the form of a rechargeable battery.

After this, preferably one or more covering layers 6 made of an insulating compound are applied to the printed circuit board 1 that is connected to the heating resistance wire 2, for example, by casting an insulating compound that can be hardened into a casting mould holding the printed circuit board 1. In this way, a sandwich body 8 results, in which the printed circuit board 1 is integrally connected to the covering layer 6 and the heating resistance wire 2 is held in position in a wiring level between these, as can be seen in FIG. 3. The heating wire is, so to speak, arranged in its own layer. Alternatively, the heating wire can also be laid in the printed circuit board only in areas, in order to heat structural components selectively.

Particularly preferably, the heating resistance wire 2 essentially extends across the entire surface of the printed circuit board 1 in a meandering way. In the case at hand, therefore, a combination of an electric circuit in the form of etched strip conductors with a heating resistance wire 2 is realised on the printed circuit board 1. According to a further embodiment, the electric circuit could also be realised by conductors, however, which then run between the connection points arranged on the printed circuit board 1 for the electronic components of the circuit.

According to an alternative, the etching of the copper film attached to the surface of the printed circuit board 1 can also always be done after the laying or wire-printing of the heating resistance wires 2, in order to work the connection points 4 out of the copper film. Because these are, however, already known ahead of time according to the existing circuit layout, the connections of the heating resistance wires 2 and connection points 4, which do not actually exist at the time, can already be produced in advance. Furthermore, the surface of the printed circuit board 1 provided with the heating resistance wires 2 can be provided with the covering layer 6 by means of pressing a prepreg made of an insulating compound to the printed circuit board 1. 

1. Printed circuit board or card comprising an electric circuit, with at least one electrically conductive heating wire that is arranged on or in the printed circuit board or card and that can be connected to a voltage source, said heating wire being attached to the printed circuit board or card by means of wire-printing, wherein heating wire has electrical insulation
 2. Printed circuit board card according to claim 1, wherein heating wire is arranged between the printed circuit board or card and a layer of insulating compound in a wiring level.
 3. Printed circuit board card according to claim 2, wherein the heating wire is formed by a resistance wire.
 4. Printed circuit board card according to claim 1, wherein the heating wire essentially extends across the entire surface of the printed circuit board or card in a meandering way.
 5. Printed circuit board or card according to claim 1, wherein the heating wire connects connection points that are arranged on the printed circuit board or card and that are for the voltage source to one another.
 6. Printed circuit board or card according to claim 2, wherein the heating wire is formed by a resistance wire. 